Method of and liquor for producing tanned leather



Patented June 16 1 925. I

UNITED STATES I 1,541,819 PATENT OFFICE.

DANIEL DANA JACKSON AND ALLEN ROGERS, or BROOKLYN, AND TE-PANG now, or NEW YORK, N. Y.

METHOD OF AND LIQUQR FOR PRODUCING TANNED LEATHER.

No Drawing.

have invented certain new and useful Im-' provements in Methods of andLiquor for Producing Tanned Leather, of which the following is a specification.

This invention relates to a tanned leather product, and to a method of tanning, and aims to provide improvements therein.

It has heretofore been proposed to tan hides and skins by the use of iron salts, but such methods as have heretofore been employed have not produced a satisfactory tanned product, the leather so produced being hard and stiff, and having a spotted appearance, shrinking and curling when dry, easily cracking on bending, deteriorat-' ing or rot-ting on keeping or storage, and being unfavorably affected by ordinary heat and light.

The'present invention provides a method of tanning. hides and skins, by the use of iron salts, whereby a good, useful leath r may be obtained, which leather compares favorably, in its properties and appearance, with bark-tanned leather, or with chrometanned leather.

The invention further provides a leather, as the product of the present process, which is full and soft, which does not shrink or curl when dried, which, when dry, has a uniform color, free from dark, hard spots, which is not brittle, and does not crack on the grain. on sharp folding, which shows no deterioration on keeping or exposure to ordinary light or heat, which will not be detanned in contact with water, and which can be dyed, colored; or subjected to such dressing or currying operations as are, or may be, usually applied to leather tanned by other methods of tanning.

The invention further provides a method of producing a white tanned leather, by the use of iron salts, "in conjunction with-other salts, and a white leather product resulting from said method.

The invention also provides a method of Application filed September 2, 1921. Serial No. 498,049.

Q tanning with iron salts, capable of application in conjunction or combination with other kinds of tanningsuch as vegetable tanning and oil tanning.

The invention further provides a novel tanning'liqlior. i

, According to the present invention, the hides or skins are treated in a tanning liquor containing ferric salts, and the ferric state is maintained throughout the period in which the. hide is in the tanning liquor, by a suitable oxidizing agent, conveniently in to excess of the quantity for complete' oxidation of the ferric salt, and by an after oxidation, as described hereinafter. According to our theory, the iron is combined with the hide in the ferric state, and the production of a satisfactory iron-tanned leather is due to the combination of the iron with the leather in a ferric state, and the maintenance of such conditions that the iron remains in such state until the tanning is completed.

The basicity of the ferric salt liquor is also to be considered, as it has been found to be important to start with such conditions of basicity that, when the hide or .skin comes into contact with the liquor, no deposition of ferric oxid, as such, will take place on the hide, as is the case where a too basic liquor is used.

The general limits of-basicity, we have found, on the basis of the ratio of the ferric iron to the mineral acid radical in the liquor, to lie between ratios of "5 equivalents of the acid radical to 6 equivalents of the ferric iron, and 8 equivalents of the acid radical to equivalents of the ferric iron. In terms of laboratory analysis, this degree of basicity is conveniently taken as representing a mean of 30 c. c. of tenth normal sodium hydroxide for each c. c. of the iron liquor containing 0.1gFe O to a c. 0.

These limits of basicity of the tanning liquor are of importance, because, if the liquor employed is more acid than that indicated by the above mentioned limits, a permanent tanning action will not take place, whereas, if the liquor is lessacid than indicated, a rapid precipitation of ferric oxid,

on the hide or skin, will occur.

Heretofore, a too basic iron liquor has been employed, with the result that much light-yellow powder was precipitated in the liquor. A greater part of this precipitate oil.

was deposited on the hide, imparting to it a light-yellow pigment color within a very short time (about 15-2O minutes in drum tanning). This mechanically deposited powder has no tanning property, and, further, prevents the tanning salt from penetrating to the interior of the hide, which, hence, may remain untanned. Consequently, a hard, stiff, brittle, under-tanned leather was produced.

A further quantity of the oxidizing agent is preferably added at or near the end of the tanning operation, conveniently an amount corresponding to the 1015% excess previously added. The oxidizing agent last added has the further advantagethat the oxidation produced thereby serves to reduce the acidity produced during the tanning, and thereby conduces to the better fixation of the iron in the hide.

After the tanning has been completed under the foregoing conditions, the hide or skin is treated to neutralize the acid in it. This may be'carried out in the tanning bath, or in a separate bath. It is preferable to effect the neutralization slowly and gradually, and it is further best to use a mild alkali, or, preferably, to use more than one alkali, starting with the milder alkali, such as borax, sodium bicarbonate, or the like, afterwards making use'of stronger alkalies.

After the hide or skin has been tanned, as described, and neutralized, it may be subjected to dressing or currying, or to combination tannage.

The dressing or currying may consist in the usual drying, rolling, stuffing, fat-liquoring, coloring, skiving, etc.

For oil combination tannage the iron tanned leather may be retanned in oil, as, for example, cod liver oil, shark liver oil, or other (marine) drying fish oil. Such oil combination tannage is particularly suitable for the production of heavy leathers, such as lace leathers, etc., where strength and tenacity are desired. Oil combination tannage may be effected by taking the iron tanned leather and* drying it to a sammied state (or sammying it back from crust), and drumming it for 4 to 6 hours in 20 to 30% of its weight of the fish oil, and afterwards hanging it out to dry.

To produce stufied leather,the iron tanned leather may be treated with a mixture of stearin, olein, and sulphonated cod liver The leather may be drummed in this mixture, heated'to about 140 degrees F., for about one-half hour. The stuffed leathers are suitable for harness, belting, etc., and the proportions of the oils may be varied, according to the particular use to which the leather is to be put.

For vegetable combination tannage, the iron tanned leather may be retanned in a tannin-liquor obtained from hemlock, quebracho, chestnut, or other ordinary wood or bark used for the purpose. Such a liquor may be made by dissolving 10% of the solid powder (or 15% of the commercial extract),

by weight, in enough water to give 1525 Barkom'eter at a temperature of 90110 F. The iron tanned leather may be drummed in this liquor for about 2 hours, or the tanning may be carried out in a vat or paddle. Grey to black leathers are advantageously produced by this vegetable combination tannage. Moreover, the vegetable combination tannage is of especial advantage in the tanning of skins and the lighter weight hides, as it gives a fuller and heavier leather; and, at the same time, it may be utilized to effect a coloring of the leather. By using less astringent tannins, such as gambia, mimosa, sumac, pure oak, or spruce extract, a brownish-grey to greyish-black color is obtained, depending on the kind of vegetable tannin used, the concentration of the liquor, and the duration of the tanning.

For dyeing the iron tanned leather, ordinary acid, basic, direct or alizarine dyes can be used. For the case of basic dyes, and advisedly in the case of acid dyes, vegetable mordants, such as fustic, mimosa, gambia, or other vegetable tannins which do not produce a decided black with iron may be used, and the colors applied as usual. No such mordants are required for direct or alizarine dyes. Black leather is preferably produced, as explained above, by combination vegetable tannage, and, where a deep black is desired, the combination tanned leather may betopped with a black dye, as per example basic leather black. The temperature of the dye bath should preferably not exceed 140 F., between 130 and 140 F. being convenient limits.

The following is a description of one particular example of themethod of carrying out the iron tannage according to the present invention.

The tanning liquor may be prepared as follows: Ferrous sulphate crystals (copperas), of 12 to 14% of the weight of the drained hide or skin to be tanned, is placed in 1 to 1% times its weight in water. It is not necessary that the amount of water used be sufficient to dissolve completely all of the ferrous sulphate, inasmuch as the ferric sulphate that is formed when the ferrous sulphate is oxidized, as presently explained, has a higher solubility, 11101 for mol, than the ferrous sulphate. This condition as regards solubility may be utilized when a strong iron liquor is desired.

The ferrous salt is then oxidized to theferric state, by any suitable oxidizing agent. Chlorine, for example, may be used. Chlorine has an advantage as an oxidizing agent, in that it may be used in the cold, or at a slightly elevated temperature, between and 110 F., for example. It is also preferable to carry out the oxidation in a closed tank, and t admit'the chlorine under a small pressure, to pounds gauge per square inch, for example). The use of chlorine as an oxidizing agent has the further advantage that no acid requires to be added to nitric acid and sulphuric acid, may also be used as oxidizing agents, in which case, however, a bolhng temperature is required. After the oxidized iron salt solution has been prepared, its basicity is regulated. For

to 2 pounds of salt per gallon of the liquor.

Instead ofthe above liquor, a tan liquor may also be prepared from a plain ferric salt, such as ferric chloride, ferric sulphate, etc. Ferric chloride yields a more stable liquor than ferric sulphate. and the liquor has very little tendency to deposit hydrated ferricoxide in the basic solution. But it has perhaps a somewhat stronger oxidizing action than the ferric sulphate liquor.

The hides or skins, after being given the usual treatment prior totanning, for example, soaking, unhairing, fleshing, washing, hating, pickling, as the case may be, are placed in the oxidized iron tanning liquor, prepared as above described. Approximately three gallons of the liquor, prepared according to the proportions set out above, is sufficient to tan 100 pounds of hide or skin. Conveniently, the liquor and hides are placed in a drum, and the drum rotated to secure a thorough working of the liquor into the hide. It is preferable, in drum tanning, to dilute the tanning liquor, prepared as above described, to from 6 to 9 times its volume. It is also advisable, before starting the tanning operation, to rinse the drum with a small quantity of bleaching powder.

The hide or skin is first worked'in the drum for from one to one-and-a-half hours, at the end of which period a small quantity of an oxidizing agent, in solution, is introduced into the drum. The oxidizing agent may be conveniently bleaching powder, and the quantity of the bleaching powder used in the solution which is introduced into the drum at this stage of the tanning operation may be from 1 to 2% of the weight of the hide or skin. If sodium bic-romate be used as the oxidizing agent, about A; to thereof, based on the weight of the hide, is

' rinsed in the drum.

used. If other oxidizing agents be used, an amount equivalent to the sodium bichromate should be taken. The oxidizing agent which is used at this stage should be one which is able to effect oxidation with a low acidity.

The working of the hide or skin in the drum is then continued for ten or fifteen minutes longer.

At the end of this time, the neutralization of the acid in the hide or skin is begun.

This is Conveniently effected in the drumv by the addition of an alkali having a mild action, For example, 4% of sodium carbonate, based on the weight of the hide, or 7% of sodium bicarbonate, or 12% of borax, dissolved in a small quantity of water, is preferably slowly, and in small portions at a time, introduced into the drum, conveniently while the drumis running, and through the trunnion.

\Vhen several alkalies are used, it is preferable to use first the milder alkalies; in the case of the alkalies mentioned above, it"is .best to first introduce the borax or sodium bicarbonate solution, and, afterwards, use the solution of sodium carbonate.

In place of sodium carbonate, a suspension of calcium carbonate or magnesium carbonate, in somewhat less quantity, may be employed. These alkaline earth carbonates possess the advantage that an excess of them can be used without harm, and that this excess, when taken up by the leather, has a softening effect, and effectively prevents the presence of sulplmric'acid in the leather.

-Owing to the strong coagulating effect which these alkaline earth carbonates have on the basic'ferric salt, it is best to start with a weak alkali and introduce the alkaline earth carbonates toward the end of the neutralization step. I

Only from to 80% of the theoretical quantity of .the total alkali necessary to neutralize the acid in the liquor is needed, the balance of the acid being permanently fixed in the hide or skin.

After the addition of the neutralizing agent or agents has been completed, the hide or skin is worked in the drum for about ten minutes longer, and then conveniently Thereafter, it may be drained and dried in the usual manner for dressing or finishing leather.

ning, with iron and phosphate salts, to produce white leather:

The hides 0r skins are first treated with the iron tanning liquor, prepared as above described, and containing the before described amount of alkali to provide the proper basicity, and also the amount of so dium chloride previously mentioned. The treatment is preferably carried out in a drum, in which the hides or skins are worked for about 1 to 1 hours.

At the end of this time, there may be introduced a solution containing 4% of sodium pyrophosphate, with 2 70 of sodium carbonate, the percentage being based on the weight of the hides or skins. The addition ,of this solution is preferably effected gradually. Instead of the pyrophosphate, any other soluble phosphate, or even a sparingly soluble phosphate, such as calcium phosphate, may be used. For example, trisodium phosphate may be used (6%), together with 1 of sodium carbonate, or di-sodium phosphate may be used (5% together with 2 of sodium carbonate). Instead of the sodium carbonate, an equiva lent amount of any other alkali may be used, as, for example, sodium bicarbonate, borax, etc.

After the phosphate solution has been all added, the treatment or working of the hide or skin in the drum is continued for 10 to 15 minutes, after which it ,is rinsed, and is ready for the usual dressing or finishing treatment.

The relative proportions of the phosphate and alkali can be varied, according to the character of the leather to be obtained.

Another mode or example of carrying out the tanning, to produce white leather, is as follows:

The oxidized iron liquor, prepared as previously described, may have added to it a phosphate solution, as, for example, 41% sodium pyrophosphate, and the hides or skins treated in this, preferably in a drum, in which case the solution is diluted, as previously described. The duration of the treatment in the drum is from 3 to 5 hours.

The addition of the sodium phosphate solution serves to provide the proper basicity of the solution, so that the addition of alkali, for this purpose, is unnecessary.

Thereafter, the hides or skins are neutralized with-2V to 4% of sodium carbonate,

or an equivalent amount of another alkali.

After rinsing, the hides or skins may be finished or dressed as usual.

While several particular modes of carrying out the process have been described, the invention is not to be understood as limited thereto, as the inventive ideas may be carried out in other particular modes.

What is claimed is:

1. A method of tanning, comprising oxidizing a ferrous salt solution to the ferric state, and adding an alkali to produce a basicity between ratios of 5 to 6 and 3 to 4: equivalents of the mineral acid radical to the ferric ion, and treating the pelt in said oxidized solution.

2. An iron: tanning liquor, comprising a solution of an iron salt, completely in the ic state, and an oxidizing agent for preventing reduction of the iron, said solution having a basicity between ratios of 5 to 6 and 3 to 4 equivalents of the acid radical to the ferric iron.

3. An iron tanning liquor, comprising a solution of an iron salt, completely in the ic state, and an oxidizing agent for preventing reduction of the iron and a .phosphate, said solution having a basicity between ratios of 5 to 6 and 3 to l equivalents of the acid radical to the ferric iron.

4. A method of tanning, comprising oxidizing a ferrous salt solution to the ferric state, and adding an alkali to produce a basicity between ratios of 5 to 6 and 3 to at equivalents of the mineral acid radical to the ferric ion, treating the pelt in said oxidized iron solution, and adding further quantities of the oxidizing agent towards the end of the treatment.

5. A method of tanning, comprising oxidizing a ferrous salt solution to the ferric state, and adding an alkali to produce a basicity between ratios of 5 to 6 and 3 to 4: equivalents of the acid radical to the ferric ion, treating the hides in said oxidized iron solution, adding further quantities of the oxidizing agent towards the end of the treatment, and neutralizing the acid in the elt.

p In witness whereof we have hereunto signed our names.

D ANIEL DANA JACKSON. ALLEN ROGERS. TE-PANG HOU. 

